Table 2.

Adjusted mortality hazards ratios associated with provider visit frequency

Visit Frequency	Cox Proportional Hazards Modela		Time-Variable Cox Proportional Hazards Modelb		Instrumental Variable Analysisc
	AHR (95% CI)	P	AHR (95% CI)	P	Probability Difference (%)d	P
<4 visits/mo	1		1
4 visits/mo	0.98 (0.96–1.01)	0.16	0.98 (0.96–1.00)	0.05	0.07	0.88

AHR, adjusted hazard ratio; CI, confidence interval.

^aAdjusted for age, sex, race, ethnicity, primary cause of ESRD, year of dialysis initiation, comorbidity score, socioeconomic status, dual eligibility status, urban status, number of dialysis sessions during run-in, hospitalization days during run-in, body mass index, estimated GFR, hemoglobin, and albumin at dialysis initiation (1 year follow-up).

^bExposure variable updated every 3 months. Adjusted for age, sex, race, ethnicity, primary cause of ESRD, year of dialysis initiation, comorbidity score, socioeconomic status, urban status, number of dialysis sessions during run-in, hospitalization days during run-in, body mass index, estimated GFR, hemoglobin, and albumin at dialysis initiation. Comorbidity score, number of dialysis sessions (compliance), and number of hospitalization days were updated every 3 months. Follow-up until December 31, 2009.

^cBivariate probit models for different outcomes adjusted for age, sex, race, ethnicity, primary cause of ESRD, year of dialysis initiation, comorbidity score, socioeconomic status, dual eligibility status, urban status, number of dialysis sessions during run-in, hospitalization days during run-in, body mass index, estimated GFR, hemoglobin, and albumin at dialysis initiation.

^dProbability difference of corresponding event when there are at least four visits in the run-in period compared with less than four visits given other covariates evaluated at the mean values.